The printer liquid ink is composed of a coloring agent and a liquid vehicle and used in printing media for impact type selective printers such as a typewriter using type set and a wire dot printer. Such printing media include, for instance, a fabric ink ribbon using a nylon woven cloth or the like as a ribbon material, and an ink roll or an ink-retaining element for supplying an ink to a fabric ink ribbon, types, etc.
The printer solid ink is composed of a coloring agent and a solid vehicle. The ink includes a heat transferable solid ink which is softened or melted upon heating to be transferred, and a pressure-sensitive transferable solid ink which is transferred upon being subjected to a pressure. The former is used in printing media for thermal transfer type selective printers equipped with a head such as a heating head, a laser head or a head for supplying electric current. The latter is used in printing media for impact type selective printers such as a typewriter using type set and a wire dot printer.
Such printing media include, for instance, a one-time thermal transfer ink ribbon wherein a homogeneous layer of a heat transferable solid ink is formed on a film foundation; a multi-usable thermal transfer ink ribbon wherein on a foundation is formed a porous layer containing a heat transferable solid ink or a heat transferable solid ink layer containing a barrier material; and a one-time pressure-sensitive transfer ink ribbon wherein a homogeneous layer of a pressure-sensitive transferable ink composition is formed on a film foundation.
Heretofore, this type of ink composition uses such triphenylmethane dyes as mentioned below, as a main component of the coloring agent thereof. The reason is that the dyes have a high tinting strength or that the dissolution or dispersion of the dyes into a vehicle can be made ready by converting them to bases. ##STR2##
In the above, Y.sup.- represents a counter ion. The ion Y.sup.- widely used is residues of organic acids such as oleic acid.
There are also used lake pigments derived from the above-mentioned triphenylmethane dyes, including C.I. Pigment Green 4 (C.I. 42000:2), C.I. Pigment Violet 39 (C.I. 42555:2), C.I. Pigment Violet 3 (C.I. 42535:2) and C.I. Pigment Violet 27 (C.I. 42535:3).
However, the above-mentioned triphenylmethane dyes and the lake pigments thereof undergo oxidation decomposition with the passage of time to change to Michler's ketone mentioned below. The Michler's ketone has a carcinogenesis (see "Bioassay of Michler's Ketone for Possible Carcinogenicity", National Cancer Institute Carcinogenesis Technical Report Series, No. 181, 1979, U.S. Department of Health, Education and Welfare Public Health Service National Institute of Health). ##STR3##
Therefore, in the case of using an ink containing the above-mentioned triphenylmethane dye or the lake pigment thereof as a coloring agent, there is the danger that Michler's ketone is incorporated into a human body to become a carcinogen due to contact of the human body with an ink or printed matters obtained using the ink in the preparation of the ink, the production of printing media, the storage of the printing media, printing with using the printing media, or thereafter, or due to the sublimatiom or volatilization of Michler's ketone formed by the oxidation decomposition.
Recently, from the viewpoint of saving of resources, there is the tendency that waste paper is regenerated to be used again. However, when printed matters contain the triphenylmethane dye or the lake pigment thereof, or Michler's ketone derived therefrom, the paper regenerated therefrom inevitably contains carcinogen.
In view of the above-mentioned, it is an object of the present invention to provide a liquid or solid ink composition for a printer which does not possess carcinogenesis and is safe in spite of using a triphenylmethane dye or a lake pigment derived therefrom.